Dominique Salm (right) may have saved Alex Allan's life after finding him in a coma 'covered in blood'

Neighbours said yesterday that Miss Salm, 35, may have saved his life. She told them she encountered a horrifying scene, with Mr Allan slumped unconscious and 'blood everywhere'.

Whitehall sources insisted yesterday there was no evidence of foul play - and blamed his collapse on pneumonia. But this does not chime with Miss Salm's account of what she found.

Experts say pneumonia sufferers may cough up some blood but rarely large amounts. Miss Salm's account of the events is likely to fuel speculation over whether Mr Allan was a target for foreign agents.

Meanwhile her mother, Sally Ann Salm, added to the intrigue by declaring: 'Some very serious people have asked Dominique not to comment on any of this until it has been fully investigated and she is doing just that. So am I.'

One of Miss Salm's neighbours said: 'Apparently there was blood everywhere. Dominique has a set of keys for Alex's home because she works there during the week.

'On Saturday Alex went cycling, which he does every weekend. On Sunday she knew he was in bed because she could hear him snoring but she does not like to interfere with his life. She later went home.

'But she was rung up by Alex's mother or sister who live in Hampshire who asked her if she could go and check on him because she's the only one who has a key apart from him. They wanted her to see what was the matter with him.

Free spirit: Alex Allan made headlines when he windsurfed to work in the 1980s to get round a train strike

'I think they knew he wasn't very well because he phoned them. She came round in the car. She was horrified because he was unconscious. She called an ambulance.'

Miss Salm is understood to have expressed regret that she didn't check on him the day before.

'But she just thought he was having a rest,' said the neighbour. 'Dominique rang up to say she didn't think he had been drugged, she thought he was just ill.

'The paramedics were in there for ages and then they went off late on Monday and that was the end.

'We didn't know what was the matter with him. The next day all the police came and were looking round his house. There was a chap watching all day, standing guard. They were there the whole afternoon.

'Dominique had washed the sheets and things but she couldn't get them out of the washing machine because she was not allowed.'

One of Whitehall's most colourful characters, Mr Allan once windsurfed down the Thames in a suit and bowler hat to avoid a train strike during the Eighties.

Described as outgoing and ebullient, friends say he revels in the unconventional.

He lives among a handful of painters, sculptors, jewellers and print-makers in a dedicated artists' colony in Hammersmith, West London, which was set up in the Sixties by the late surrealist painter Julian Trevelyan, who gave away land next to his home to a group of hard-up artists.

Seven homes with spacious studios were built and a restrictive covenant, stipulating that only working artists be allowed to live there, is still in force today.

It is understood Mr Allan's living arrangements were reviewed by the police after he was appointed to the Joint Intelligence Committee last November.

Relaxed: Grateful Dead fan Alex Allan posted old pictures on his website. Friends say he 'revels in the unconventional'

Miss Salm declined to talk to The Mail on Sunday. She describes herself as being 'passionate about art and wildlife' and combines her love of both 'to build a reputation both nationally and internationally as a skilled wildlife artist'.

She was born in Jamaica but moved to Hampshire when she was a child. Miss Salm is a regular visitor to her mother's £1million country home in the picturesque village of Kingsclere.

Last night a Whitehall source said: 'There is nothing to suggest this is anything other than a tragic illness.'

A police source said that officers had examined the circumstances in which Mr Allan was found and 'quickly established there were no indications of anything suspicious'.

He added: 'Because he is a person of significance, investigators made sure nothing untoward had occurred. But it was quickly established there was a medical reason for how he was found. He is being treated as a medical patient not the victim of any kind of poisoning or other attempt on his life.'

Dr Keith Prowse, chairman of the British Lung Foundation, said it was not unusual for someone of Mr Allan's age and lifestyle to succumb to pneumonia. But pneumonia alone would not have produced much blood

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'If it is pneumonia it is likely to be secondary to something else. And a significant quantity of blood is more likely to come from the gut than the chest,' he said.

'Pneumonia is something that can strike very quickly, however.'

But the only official comment about Mr Allan's condition has come from Scotland Yard who said it was a 'non suspicious medical emergency.'

A Whitehall source added that Mr Allan was under police guard in a Central London hospital.

As one of the Government's most senior security advisers, Mr Allan oversees the committee which analyses intelligence information coming in from MI5, MI6 and GCHQ, as well as from the military and other sources.

In this role he has the highest level of security clearance and access to top secret files on terrorism and counter-espionage.

Other staff at his security level have their identities protected but, like Jonathan Evans, the head of MI5, and John Scarlett, the head of MI6, the chairman of the JIC is a public figure.

However Mr Allan, who was previously private secretary to both John Major and Tony Blair and head of several Government departments, has always been extremely open about details of his personal life.

He has previously revealed his home address, telephone number and mobile number on the internet.

He also published a detailed personal website, which he last updated on Saturday June 28. A rock fan, he calls himself a 'Deadhead', slang for a die-hard fan of American band the Grateful Dead.

His website contains a Grateful Dead 'song finder' and photographs of his family and friends. Among the pictures is one of him cycling and another strumming a guitar.

The details on the site are likely to have caused concern to security chiefs as they would enable the foreign intelligence services to form a comprehensive overview of his activities, interests, family and friends.

Yesterday the Cabinet Office refused to discuss whether Miss Salm had been security cleared, her relationship with Mr Allan or 'any aspects of his security arrangements'.